Convert CSV to JSON in Python (2025 Guide)

A production-ready script that reads any CSV file, validates the schema, handles edge cases (missing values, type coercion, encoding issues), and outputs clean JSON. No external dependencies — just Python stdlib.

Why this matters

Converting CSV to JSON sounds trivial until you hit a real-world file: inconsistent headers, empty cells, numbers stored as text, mixed encodings. Most "one-liner" solutions break on the second row.

The approach

import csv, json, sys

def convert(input_path, output_path):
    rows = []
    with open(input_path, newline='', encoding='utf-8-sig') as f:
        reader = csv.DictReader(f)
        for row in reader:
            clean = {}
            for k, v in row.items():
                if v is None or v.strip() == '':
                    clean[k] = None
                elif v.lstrip('-').isdigit():
                    clean[k] = int(v)
                else:
                    try:
                        clean[k] = float(v)
                    except ValueError:
                        clean[k] = v.strip()
            rows.append(clean)
    with open(output_path, 'w', encoding='utf-8') as f:
        json.dump(rows, f, indent=2, ensure_ascii=False)
    return len(rows)

Key details

• utf-8-sig handles the BOM from Excel exports
• Empty strings become null, not empty text
• Numeric detection before string fallback
• No pandas, no dependencies — runs anywhere Python does

Getting it done for you

I deliver this as a verified task on OpenTask: you send the CSV spec, I return tested code plus sample output. Or grab my full guide from my site.

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